Tuesday, September 8, 2009

On situations and events

Almost midnight, after a long day that started in 8AM and did not end until now.... some days are like that, tomorrow might be a slightly shorter work day. Before retiring to sleep, I'll write something on this Blog as a kind of doing something else...

I have written before about situations, however, I am not sure that this term is still well understood (the same applies for context, but I'll leave context for another posting). In the EPIA book, when revising the book, we decided that the term situation is a very basic one in event processing, and put it in the introduction chapter. Situation can be thought of as event that requires reaction, but this is somewhat simplistic definition, since indeed situation is an event, but it is something that is considered as event in the user's domain, and not necessarily an event in the physical domain. Sometimes we wish to react to a raw event, sometimes we can say that a derived event represent the circumstances which we want to react, and sometimes a derived event is just approximation for the situation.

Let's look at a couple of example.

Example 1: The situation we would like to react is that a driver crosses toll both without paying -- In Israel, as high-tech country, in the only toll highway, we have camera that takes pictures of the license plate and send the bill to the driver (unless one is subscriber and then it has some identification device in the car), thus we don't really have toll booths, but in the USA it is quite pervasive. Anyway -- this situation can occur if a driver moved through "EZPASS" lane without having a device, or somehow sneaks without paying. Assuming that there are cameras that capture it, then the derived event, which is a disjunction pattern of these two events, is a complete match for detecting the situation.

However, life is not that simple, and we move to example 2. This example, that I used before in different opportunities, is that in a call center we are looking for frustrated customers in order to send a friendly customer relations officer to call them and ease their frustration.
Sometimes the person who handles request can detect the frustration, by the tone of the voice, if it is a phone call, or style of writing, if Email, but sometimes not, so what we can do is based on past experience, devise criteria for who is frustrated customer, and this may be -- a customer that sent three requests on the same topic during a single day. This criterion may be an approximation for the "frustrated customer" situation, but not an exact match, thus we can get false positives or false negatives. Handling such approximation cases is part of inexact event processing, and this seems to be one of the issues that will be part of the next generation of event processing languages and models. More - Later.

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